The invention relates to a Pd/Ni WO3 (palladium/tungsten-doped nickel oxide) anodic double layer gasochromic device in which the palladium layer functions as a catalyst material that facilitates reaction with hydrogen gas. The hydrogen gas is disassociated on the Pd catalyst into H atoms, which diffuse into the Nixe2x80x94WO3 film. The Nixe2x80x94WO3 thin film exhibits an anodic coloration with H+ or Li+ insertion. The Nixe2x80x94WO3 thin film is more stable than WO3 films in air, due to the fact that Ni oxide based materials, unlike WO3, forms a hydroxide upon absorption of water vapor. Even after forming the hydroxide, the Nixe2x80x94W hydroxide thin film still shows a strong color change. By use of the gasochromic response upon exposure to hydrogen gas, hydrogen gas monitoring of the anodic double layer device of the invention can be detected via optical detection schemes such as a fiber-optic type H2 sensor.
1. Background Art
Hydrogen is a plentiful, clean, non-polluting fuel. Hydrogen is currently used in many industries, and the US demand for hydrogen is approximately 140 billion cubic feet per year and growing. However, hydrogen is explosive at 4% in air. Therefore, it is critical to measure, monitor and control hydrogen wherever it is used.
In the gasochromic art where sensors and measurement instrumentation for hydrogen gases detect and/or measure hydrogen, typically there is required a portable sensing device, a kit (where hydrogen gas detection and/or measurement is required in existing equipment), and sensor heads installed at points where hydrogen leaks are possible, or where monitoring is necessary (i.e., in internal combustion engines which operate using hydrogen as a fuel).
The problems associated with current H2 gasochromic devices are that these devices are not of adequate durability in that they degrade quickly with cycling and time, are too moisture sensitive, and react too slowly in response to the presence of H2 to produce an optical absorption change with a lengthy time constant in the vicinity of 30 seconds.
2. Description of the Related Art
At present, optical detection of H2 is widely accomplished through the use of Pd/WO3 hydrogen detecting gasochromic devices. However, several problems or drawbacks are associated with the use of Pd/WO3 hydrogen detecting gasochromic devices. These problems are: they are of inadequate durability; they respond slowly to the presence of H2; and there is a conflicting cathodic-anodic optical response that results in a weak color change.
Inadequate durability problems are occasioned by the fact that the Pd/WO3 hydrogen detecting gasochromic device degrades quickly with cycling and time, and is unduly moisture sensitive.
The slow response of the Pd/WO3 hydrogen detecting gasochromic device in the presence of a H2 leak is due to the hydrogen reaction in HxWO3 which produces a slow optical absorption change within a lengthy room temperature time constant of about 30 seconds.
Also, there is a conflicting optical response upon detection of H2 by the Pd/WO3 gasochromic device due to the fact that the WO3 exhibits a cathodic response and the Pd exhibits an opposite anodic response.
3. Disclosure of Invention
One object of the present invention is to provide an anodic double layer H2 detecting gasochromic device of improved durability that shows little degradation with cycling and time.
A further object of the present invention is to provide an anodic double layer H2 detecting gasochromic device that responds more swiftly to detection of H2 gas by producing faster optical absorption change within a room temperature time constant of about 10 seconds.
Another object of the present invention is to provide an anodic double layer H2 detecting gasochromic device comprising complementary coloring layers in which both of the layers consist of an anodic coloration material.
In general, the invention is accomplished by providing a palladium/tungsten-doped nickel oxide anodic double layer gasochromic device in which, a Nixe2x80x94WO3 thin film is prepared on a glass substrate by reactive sputtering. Thereafter, a palladium layer is evaporated onto the Nixe2x80x94WO3 thin film. The palladium layer serves as a catalyst material that facilitates reaction with hydrogen gas. That is, the hydrogen gas is dissociated on the Pd catalyst into H atoms, which readily diffuse into the Nixe2x80x94WO3 film. The Nixe2x80x94WO3 thin film exhibits an anodic coloration with insertion of either H+ or Li+.
The Nixe2x80x94WO3 thin films arc more stable than WO3 films in air due to the fact that Ni oxide based materials, unlike WO3, form a hydroxide upon absorption of water vapor. Even after formation of the hydroxide, Nixe2x80x94W hydroxide thin films still show a strong color change. By use of this gasochromic response upon exposure to hydrogen gas, hydrogen gas can be monitored via optical detection schemes such as fiber-optic type H2 sensors.